At present, a non-aqueous secondary battery is generally employed as an electric source for driving small electronic devices. The non-aqueous secondary battery comprises a positive electrode, a negative electrode, and a non-aqueous electrolytic solution. The non-aqueous lithium secondary battery generally comprises a positive electrode of lithium complex oxide such as LiCoO2, LiMn2O4 or LiNiO2, a non-aqueous electrolytic solution such as a solution of electrolyte in a carbonate solvent such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (MEC), and a negative electrode of carbonaceous material or lithium metal.
Also known is a lithium primary battery comprising a positive electrode of, for instance, manganese dioxide and a negative electrode of, for instance, lithium metal and showing a high energy density.
The non-aqueous secondary battery preferably has good battery performances such as large electric discharge capacity and high electric discharge retention (i.e., good cycle characteristics). However, there are observed certain problems in the known non-aqueous secondary battery. For instance, in the non-aqueous lithium ion secondary battery using a positive electrode of LiCoO2, LiMn2O4, or LiNiO2, oxidative decomposition of a portion of the non-aqueous electrolytic solution undergoes in the electric charging stage. The decomposition product disturbs electrochemical reaction so that the electric discharge capacity decreases. It is considered that the oxidative decomposition is caused in the non-aqueous solvent of the non-aqueous electrolytic solution on the interface between the positive electrode and the electrolytic solution.
Moreover, in the non-aqueous lithium secondary battery particularly using negative electrode of carbonaceous material of high crystallinity such as natural graphite or artificial (or synthetic) graphite, reductive decomposition of the solvent of the non-aqueous electrolytic solution undergoes on the surface of the negative electrode in the charging stage. The reductive decomposition on the negative electrode undergoes after repeated charging-discharging procedures even in the case of using ethylene carbonate (EC) which is generally employed in the electrolytic solution.
JP-A-3-289062 proposes to incorporate 0.2 to 10 vol. % of 1,4-dimethoxybenzene compound into a non-aqueous solvent comprising a high permittivity solvent such as ethylene carbonate (EC) or propylene carbonate (PC) and a low permittivity solvent such as tetrahydrofuran (THF) so that the cycle characteristics can be improved.
U.S. Pat. No. 5,256,504 and U.S. Pat. No. 5,474,862 propose to incorporate ethyl propionate into a combination of ethylene carbonate and diethyl carbonate (DEC) so that the cycle characteristics can be improved.
JP-A-9-161845 proposes a lithium secondary battery which employs a combination of a high activity solvent having a donor number of 14 to 20 and a low activity solvent having a donor number of 10 or lower. This patent publication describes the use of a negative electrode comprising a carbonaceous material of a graphite crystal structure having a lattice distance (d002) of lattice surface (002) of 0.3365 nanometer or more. The patent publication further describes that the high activity solvent can be a cyclic carbonate ester, a cyclic ester, a linear esher, a cyclic ether, a linear ether, or a nitrile. The nitrile can be a dinitrile such as glutaronitrile or adiponitrile. It is noted that in Example 6 the glutaronitrile is employed in an amount of 19 vol. % in a non-aqueous solvent for preparing a electrolytic solution.